Dienoic Esters Research Articles

Separation and identification of geometrical isomers of 9,12-octadecadienoic and 9,12,15-octadecatrienoic acids

Geometrical isomers of methyl 9,12-octadecadienoate and methyl 9,12,15-octadecatrienoate were fractionated by thin-layer chromatography on Silica Gel G modified with silver nitrate and ammonium hydroxide. Dienoic esters were completely separated into three classes: (1) all trans; (2) trans-cis and cis-trans; and (3) all cis. Trienoic esters were similarly separated into four classes: (1) all trans; (2) di- trans, mono- cis; (3) di- cis, mono- trans; and (4) all cis. Complete separation of the cis, trans isomers of methyl octadecadienoate and of the mono- cis, di- trans and mono- trans, di- cis isomers of methyl octadecatrienoate was achieved by gas-liquid chromatography on glass capillary columns (Apiezon L).

Preparation of 9,15‐octadecadienoate isomers

AbstractLinolenic acid was reduced with hydrazine to produce a mixture containing a max of dienoic acids. After methylation this mixture was separated into trienoic, dienoic, monoenoic, and saturated esters by countercurrent distribution (CCD) with acetonitrile and hexane. The dienoic ester was further fractionated by CCD with methanolic silver nitrate and hexane to separate purecis,cis‐9,15‐octadecadienoate and the equimixture ofcis,cis‐9,12‐ and 12,15‐octadecadienoates.Following isomerization of thecis,cis‐9,15‐octadecadienoate with selenium, the geometric isomers were fractionated by CCD with methanolic silver nitrate and hexane. Puretrans,trans and purecis,cis isomers were isolated, as well as an unresolved mixture ofcis,trans andtrans,cis isomers. The characteristics of these isomers and related compounds are compared as determined by CCD, IR absorption, and capillary gas‐liquid chromatography (GLC).